$ git clone -n https://src.fedoraproject.org/rpms/fedora-release.git /var/lib/mock/f39-build-1510921-35513/root/chroot_tmpdir/scmroot/fedora-release
Cloning into '/var/lib/mock/f39-build-1510921-35513/root/chroot_tmpdir/scmroot/fedora-release'...
$ git fetch origin c2df7f49192e0505668b21928eb63256d9cd5681:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/fedora-release
 * [new ref]         c2df7f49192e0505668b21928eb63256d9cd5681 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c2df7f4 Rebuild for final f39 release